Volumetric fog vs. Instanced stereo (deferred)

Development Rendering
, ,
1

Hi

Are there any know issues with rendering volumetric fog with instanced stereo enabled (deferred rendering, windows, dx12) in UE 5.6 ?

For us it does not render in right eye, but when doing PIX capture and replying it … the fog is there … so in capture it works.

We want to enable instanced stereo (without if vol fog works just fine) due to performance reasons.

[Attachment Removed]

2

Hello,

This could be related to a known issue with HZB (HZB occlusion is broken on Instanced Stereo) if the fog is not getting lit correctly in the right eye due to the light getting culled from the light grid. You could test this theory by seeing if r.Forward.LightGridHZBCull 0 has any effect. There was also a recent HZB fix that might be related CL#52154255 Fix HZB ViewRect extending beyond view depth in split-screen. I’m passing this along to my colleagues who are more familiar with this area for guidance

[Attachment Removed]

3

Hi Mariusz,

Nice find on that fix! Volumetric fog is not a path we test often in stereo so some bugs are expected. I’ll make a note to pull in your fix for UE 5.8.

Thanks,

Christopher Fiala

[Attachment Removed]

4

I have HZB disabled for that exact reason, and it’s not lighting problem, the problem is that all materials that have ‘volumetric’ seems to work only in left eye (we have giant cube in scene with vol material that does the fog) and as I’v bumped it color to pink, it’s shown only in left eye, not in the right one. So it’s something along those lines.

I’v used renderdoc to capture frame and ideed, voxelization is missing from right eye

[Image Removed]

[Attachment Removed]

5

View.VolumetricMeshBatches.Num() in FSceneRenderer::VoxelizeFogVolumePrimitives for the right eye is empty.

[Attachment Removed]

6

OK, I’v fixed this by adding in

void FComputeAndMarkRelevance::Finalize()

this code:

[Image Removed]seems to work.

[Attachment Removed]